The
FileSystemWatcher
has nothing to do with handling changes from a UI. It is intended to monitor changes to a file system (hence it's name). Your application needs to drive the logic to rename the file - in other words, it needs to perform a
File.Move
to rename the file from one filename to the other. Now, one thing to be aware of is that this is going to depend on the user having the relevant permissions to rename the file; depending on security, this might not be allowed, so your application design will have to take this into account.
File.Move[
^] documentation.